1. Field of the Invention
The present invention relates generally to inkjet printing. More specifically, the present invention relates to inkjet printing onto an intermediate transfer medium coated with a liquid coating solution.
2. Description of the Related Art
Early inkjet printers had several distinct advantages over laser printers. They could print in color and had size and cost advantages. However, in order for the next a generation of inkjet printers to compete with laser printers in an office environment, it will be necessary to increase the printing speed and print quality. As a goal, a printing speed of 20 pages per minute is desired. For print quality, a print density of 1.4 as measured on an optical densitometer and a resolution of at least 600 dots per inch are desired.
To achieve these goals and successfully compete with laser printers in the business printer market, it has been proposed to print from an inkjet head onto an intermediate transfer surface (e.g. a drum) and then transfer the image onto a final medium (e.g. paper). Prior attempts at this intermediate transfer type printing have resulted in poor transfer efficiency, that is, the image printed onto the intermediate transfer surface did not completely transfer to the final medium. Some of the material deposited on the intermediate transfer surface remained after transfer. Prior attempts at using an intermediate transfer medium with inkjet printing have also resulted in poor optical density.
Accordingly, it is an object of the present invention to increase the speed of inkjet printing.
It is a further object of the present invention to increase the optical density of images printed by inkjet printing.
It is a still further object of the present invention to enable inkjet printing using an intermediate transfer medium in which the transfer efficiency to the final medium is increased.
These and other objects are accomplished by providing a method of printing, which uses a liquid applicator to apply a coating solution containing polyvinyl pyrrolidone or a polyvinyl pyrrolidone copolymer to an intermediate transfer medium. An image is printed onto the intermediate transfer medium using an ink jet printing device.
The coating solution contains an organic solvent, which is preferably a glycol solvent or a diol solvent. Suitable solvents include trimethylene glycol, diethylene glycol, propylene glycol, di propylene glycol, tri propylene glycol, 1,2 butane diol, 2 pyrrolidone, gamma butyrolactone and glycerol. The coating solution is applied in an amount of 0.01 to 10 mg/cm2 and more preferably in an amount of 0.1 to 3 mg/cm2. The coating solution may contain 0.01 to 20 wt. % of polyvinyl pyrrolidone or a polyvinyl pyrrolidone copolymer, 5-95 wt. % of an organic solvent and 5-95 wt. % water. More preferably, the coating solution contains 0.01 to 15 wt. % of polyvinyl pyrrolidone or a polyvinyl pyrrolidone copolymer, 5-95 wt. % of an organic solvent and 5-95 wt. % water. Most preferably, the coating solution contains 2 to 8 wt. % of polyvinyl pyrrolidone or a polyvinyl pyrrolidone copolymer, 5-95 wt. % of an organic solvent and 5-95 wt. % water. The PVP should have a molecular weight greater than 400,000, more preferably greater than 750,000 and most preferably within the range of from 850,000 to 1,150,000.